Infusion system and method of use which prevents over-saturation of an analog-to-digital converter

ABSTRACT

To detect air in a fluid delivery line of an infusion system, infusion fluid is pumped through a fluid delivery line adjacent to at least one sensor. A signal is transmitted and received using the at least one sensor into and from the fluid delivery line. The at least one sensor is operated, using at least one processor, at a modified frequency which is different than a resonant frequency of the at least one sensor to reduce an amplitude of an output of the signal transmitted from the at least one sensor to a level which is lower than a saturation level of the analog-to-digital converter to avoid over-saturating the analog-to-digital converter. The signal received by the at least one sensor is converted from analog to digital using an analog-to-digital converter. The at least one processor determines whether air is in the fluid delivery line based on the converted digital signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/289,796, entitled “Infusion System and Method of Use Which PreventsOver-Saturation of an Analog-to-Digital Converter,” filed May 29, 2014,which claims the benefit of priority to U.S. Provisional PatentApplication No. 61/828,408, entitled “Infusion System and Method of UseWhich Prevents Over-Saturation of an Analog-to-Digital Converter,” filedMay 29, 2013, the disclosures of which are hereby incorporated byreference in their entirety.

BACKGROUND Field of the Invention

This disclosure relates to an infusion system and method of use whichprevents over-saturation of an analog-to-digital converter being used todetermine whether air is present in the infusion system.

The Symbig™ infusion system, made by Hospira, Inc., previously detectedwhether air was present in the infusion system by operating one or moresensors at their resonant frequency, which was determined and set duringcalibration. The one or more sensors were used to transmit and receive asignal through a fluid delivery line of the infusion system in order todetermine, based on the strength of the signal that propagated throughthe fluid delivery line, whether air, fluid, or some combination thereofwas disposed in the fluid delivery line. Signals propagate betterthrough liquid fluid than through air. The resonant frequency of the oneor more sensors is the frequency at which the output of the signaltransmitted from the one or more sensors is maximized for a giventransfer medium such as for the infusion fluid contained within thefluid delivery line of the infusion system. Thus, conventional wisdomsuggested that the one or more sensors would be most effective at theirresonant frequency. However, analog-to-digital converters are used toconvert the received analog signal from analog to digital in order for aprocessor to determine, based on the converted digital signal, whetherair, fluid, or some combination thereof is disposed in the fluiddelivery line of the infusion system. It has been observed or discoveredby the Applicants that under certain conditions, analog-to-digitalconverters can become over-saturated if the output of the signaltransmitted from the one or more sensors is too high.

A system and method is needed to overcome one or more issues of one ormore of the existing systems and methods for detecting air in aninfusion system.

SUMMARY OF THE INVENTION

In one embodiment, an infusion system is disclosed for being operativelyconnected to a fluid delivery line and to an infusion containercontaining an infusion fluid. The infusion system includes a pump, atleast one sensor, an analog-to-digital converter, at least oneprocessor, and a memory. The at least one sensor is disposed adjacent tothe fluid delivery line and configured to transmit and receive a signalto detect whether there is air in the fluid delivery line. Theanalog-to-digital converter is electronically connected to the at leastone sensor for converting the received signal from analog to digital.The at least one processor is in electronic communication with the pump,the at least one sensor, and the analog-to-digital converter. The memoryis in electronic communication with the at least one processor. Thememory includes programming code for execution by the at least oneprocessor. The programming code is configured to operate the at leastone sensor at a modified frequency which is different than a resonantfrequency of the at least one sensor in order to reduce an amplitude ofan output of the signal transmitted from the at least one sensor to alevel which is lower than a saturation level of the analog-to-digitalconverter.

In another embodiment, a method is disclosed for detecting air in afluid delivery line of an infusion system. In one step, infusion fluidis pumped through a fluid delivery line adjacent to at least one sensor.In another step, a signal is transmitted and received using the at leastone sensor into and from the fluid delivery line. The at least onesensor is operated, using at least one processor, at a modifiedfrequency which is different than a resonant frequency of the at leastone sensor in order to reduce an amplitude of an output of the signaltransmitted from the at least one sensor to a level which is lower thana saturation level of an analog-to-digital converter to avoidover-saturating the analog-to-digital converter. In an additional step,the signal received by the at least one sensor is converted from analogto digital using the analog-to-digital converter.

In still another embodiment, a method is disclosed for arranging andusing an infusion system. In one step, a resonant frequency of at leastone sensor is determined. In another step, a saturation level of ananalog-to-digital converter is determined. In still another step, the atleast one sensor is disposed adjacent to a fluid delivery line. In yetanother step, a pump is connected to the fluid delivery line. In anotherstep, the analog-to-digital converter is electronically connected to theat least one sensor. In an additional step, at least one processor iselectronically connected to the pump, to the at least one sensor, and tothe analog-to-digital converter. In still another step, the at least oneprocessor is programmed to operate the at least one sensor at a modifiedfrequency which is different than the resonant frequency of the at leastone sensor in order to reduce an amplitude of an output of a signaltransmitted from the at least one sensor to a level which is lower thanthe saturation level of the analog-to-digital converter to avoidover-saturating the analog-to-digital converter.

The scope of the present disclosure is defined solely by the appendedclaims and is not affected by the statements within this summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the disclosure.

FIG. 1 illustrates a block diagram of an infusion system under oneembodiment of the disclosure;

FIG. 2 is a graph illustrating in one embodiment of the disclosure howshifting the frequency of a sensor of the infusion system of FIG. 1 to amodified frequency which is different than the resonant frequency of thesensor may avoid over-saturating an electronic detection device of FIG.1;

FIG. 3 illustrates a cross-section through one embodiment of a segmentof fluid delivery line coupled to an electronic transmitting device, atransmitter portion of a sensor, a receiver portion of the sensor, andan electronic detection device;

FIG. 4 illustrates a top view through one embodiment of thepiezoelectric crystals of the transmitter portion of the sensor of FIG.3;

FIG. 5 illustrates a flowchart of one embodiment of a method forarranging and using an infusion system;

FIG. 6 illustrates a flowchart of one embodiment of a method fordetecting air in a fluid delivery line of an infusion system;

FIG. 7 is a graph illustrating five different curves showing for fivedifferent illustrative sensors, which could each be tried as the sensorin the infusion system of FIG. 1, how their respective signal strengthvaries as their modified frequency varies; and

FIG. 8 illustrates a flowchart of one embodiment of a method fordetermining the modified frequency of an infusion system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is of the best currently contemplatedmodes of carrying out the disclosure. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the disclosure, since the scope of thedisclosure is best defined by the appended claims. It is noted that theFigures are purely for illustrative purposes and are not to scale.

Applicants have discovered through testing of the Symbig™ infusionsystem that when some sensors are operated at their resonant frequencythe signal transmitted from the one or more sensors sometimes isover-saturated and causes the analog-to-digital converter to becomeover-saturated. Variation in sensor manufacturing and assembly,especially bonding of the piezo-electric element to the supporting bodyin an ultrasonic sensor, can be significant. Some piezo-electricelements may be extremely well bonded within the sensor assembly whileothers may have many gaps, voids or air bubbles in the bonding of theelement to the sensor body. Sensors with few bonding imperfections mayhave high output amplitude, particularly at resonant frequency.Applicants have further discovered that this high amplitude,oversaturated signal sometimes reduces the accuracy and reliability ofthe analog-to-digital converters which may not correctly convert thereceived over-saturated signal. Applicants have additionally discoveredthat this could lead to errors in the infusion system's determination asto whether or not air is contained in the infusion system and thegeneration of alarms.

FIG. 1 illustrates a block diagram of an infusion system 100 under oneembodiment of the disclosure. The infusion system 100 comprises: aninfusion container 102; a fluid delivery line 104; a pump device 106; aprocessing device 108; an alarm device 110 that generates an audio,visual, other sensory signal or the like to a user; an input/outputdevice 112; an electronic transmitting device 114; a sensor 116; anelectronic detection device 118; and a delivery/extraction device 120.The infusion system 100 may comprise the Plum A+™, Gemstar™, Symbig™, orother type of infusion system. The infusion container 102 comprises acontainer for delivering fluid such as IV fluid or a drug to the patient122. The fluid delivery line 104 comprises one or more tubes, connectedbetween the infusion container 102, the pump device 106, the sensor 116,and the delivery/extraction device 120, for transporting fluid from theinfusion container 102, through the pump device 106, through the sensor116, through the delivery/extraction device 120 to the patient 122. Thefluid delivery line 104 may also be used to transport blood, extractedfrom the patient 122 using the delivery/extraction device 120, throughthe sensor 116 as a result of a pumping action of the pump device 106.The pump device 106 comprises a pump for pumping fluid from the supplycontainer 102 or for pumping blood from the patient 122. The pump device106 may comprise a plunger based pump, a peristaltic pump, or anothertype of pump.

The processing device 108 comprises at least one processor forprocessing information received from the electronic detection device 118and/or the sensor 116 and for executing one or more algorithms todetermine if air, fluid, or some combination thereof is located in thefluid delivery line 104 at the location of the sensor 116. Theprocessing device 108 is in electronic communication with the pumpdevice 106, the electronic transmitting device 114, the sensor 116, theelectronic detection device 118, the input/output device 112, and thealarm device 110. The processing device 108 includes or is in electroniccommunication with a computer readable memory, containing programmingcode containing the one or more algorithms for execution by the at leastone processor, and a clock.

The alarm device 110 comprises an alarm, triggered by the processingdevice 108, for notifying the clinician (also referred to as ‘user’herein) as to the presence of air being disposed in the fluid deliveryline 104 at the location of the sensor 116. The alarm device 110 may beconfigured to stop the pump device 106 prior to an air embolism beingdelivered through the fluid delivery line 104 and thedelivery/extraction device 120 to the patient 122.

The input/output device 112 comprises a device which allows a clinicianto input or receive information. The input/output device 112 allows aclinician to input or receive information regarding the infusion. Forinstance, the clinician may use the input/output device 112 to input orselect a medication infusion program to be applied by the processingdevice 108, to set settings for the processing device 108 to apply inusing the programming code containing the algorithm(s), or to inputother type of information. The input/output device 112 may furtheroutput information to the clinician. In other embodiments, any of theinformation inputted into the input/output device 112 may bepre-installed into the programming code or the processing device 108.

The delivery/extraction device 120 comprises a patient vascular accesspoint device for delivering fluid from the infusion container 102 to thepatient 122, or for extracting blood from the patient 122. Thedelivery/extraction device 120 may comprise a needle, a catheter, oranother type of delivery/extraction device. In other embodiments, theinfusion system 100 of FIG. 1 may be altered to vary the components, totake away one or more components, or to add one or more components.

The electronic transmitting device 114 comprises electronic circuitry,connected to the sensor 116, which transmits a signal from a transmitterportion 116A of the sensor 116, through the fluid delivery line 104, toa receiver portion 116B of the sensor 116. The transmitter portion 116Aand the receiver portion 116B are disposed on opposed sides of the fluiddelivery line 104. The receiver portion 116B of the sensor iselectronically connected to the electronic detection device 118. Thesensor 116 may comprise an air-in-line sensor for sensing, with theassistance of the electronic detection device 118 and the processingdevice 108, whether air, fluid, or some combination thereof is containedin the fluid delivery line 104. The sensor 116 is disposed adjacent toand/or connected to the fluid delivery line 104 distal of the pumpdevice 106. In other embodiments, the sensor 116 may be located proximalto the pump device 106 or may be located in both proximal and distalpositions.

The transmitter and receiver portions 116A and 116B of the sensor 116sense the presence of air, fluid, or some combination thereof within thefluid delivery line 104. The transmitter and receiver portions 116A and116B of the sensor 116 comprise a transducer such as an ultrasonicsensor, an acoustic sensor, an optical sensor, or another type ofsensor. Alternate arrangements of the sensor transmitter and receiverare possible and include both side-by-side arrangements and the use of asingle transducer to both transmit and receive a reflected signal. Inother embodiments, any number, configuration, and type of sensor(s) maybe used.

The electronic detection device 118 comprises electronic circuitry,connected to the receiver portion 116B of the sensor 116, for receivingthe signal transmitted from the electronic transmitting device 114,through the transmitter portion 116A of the sensor 116, through thefluid delivery line 104, to the receiver portion 116B of the sensor 116,to the electronic detection device 118. The electronic detection device118 comprises an analog-to-digital converter which is electronicallyconnected to the sensor 116 for converting the signal received by thereceiver portion 116B of the sensor from analog to digital andcommunicating the digital reading to the processing device 108. Theprocessing device 108 then determines, based on the digital reading,whether air, fluid, or some combination thereof is disposed in the fluiddelivery line 104 at the sensor 116 by executing the programming codecontaining the one or more algorithms.

The programming code implemented by the processing device 108 isconfigured to operate the sensor 116 at a modified frequency which isdifferent than a resonant frequency of the sensor 116 in order to reducethe amplitude of an output of the signal transmitted from thetransmitter portion 116A of the sensor 116 to a level which is lowerthan a saturation level of the electronic detection device 118comprising the analog-to-digital converter. The resonant frequency ofthe sensor 116 is the frequency at which the output of the signaltransmitted from the transmitter portion 116A of the sensor 116 ismaximized for a given transfer medium (such as the fluid delivery line104 filled with infusion fluid).

By reducing the amplitude of the output of the signal transmitted fromthe transmitter portion 116A of the sensor 116 to a level which is lowerthan the saturation level of the electronic detection device 118comprising the analog-to-digital converter, the reliability and accuracyof the processing device 108 detecting air, fluid, or some combinationthereof in the fluid delivery line 104 is increased. This is becausewhen the amplitude of an output of a signal transmitted from a sensor toan analog-to-digital converter is greater than a saturation level of theanalog-to-digital converter, the accuracy and reliability of theanalog-to-digital converter is reduced which may lead to errors indetecting air, fluid, or some combination thereof in the fluid deliveryline. The resonant frequency of the sensor 116, the saturation level ofthe electronic detection device 118, and the amplitude of the output ofthe signal transmitted from the transmitter portion 116A of the sensor116, set to be lower than the saturation level of the electronicdetection device 118, each may be determined and/or set duringcalibration of the sensor 116 and the electronic detection device 118,or advantageously may be set at other times such as during use in thefield.

FIG. 2 is a graph 130 illustrating in one embodiment of the disclosurehow shifting the frequency of the sensor 116 of FIG. 1 to a modifiedfrequency which is different than the resonant frequency of the sensor116 may avoid over-saturating the electronic detection device 118 ofFIG. 1. Frequency of the sensor 116 of FIG. 1 is plotted on the X-axisof the graph 130. Output of the sensor 116 of FIG. 1 expressed as apercentage of the maximum sensor output is plotted on the Y-axis of thegraph 130. The resonant frequency 132 is the frequency at which theoutput of the sensor 116 of FIG. 1 is maximized. The electronicdetection device 118 of FIG. 1 is over-saturated when the output of thesensor 116 of FIG. 1 is above the saturation level 134. By reducing theoutput of the sensor 116 of FIG. 1 to a percentage of maximum which islower than the saturation level 134, over-saturation of the electronicdetection device 118 of FIG. 1 is avoided. As shown, this may be done bychanging the frequency of the sensor 116 of FIG. 1 to a modifiedfrequency which is different than the resonant frequency 132 to reducethe output of the sensor 116 of FIG. 1 to a level which is lower thanthe saturation level 134 of the electronic detection device 118 ofFIG. 1. For instance, at point 136 the frequency of the sensor 116 ofFIG. 1 has been increased beyond the resonant frequency 132 to reducethe output of the sensor 116 of FIG. 1 to a level which is lower thanthe saturation level 134 of the electronic detection device 118 of FIG.1 to avoid oversaturating the electronic detection device 118.Similarly, at point 138 the frequency of the sensor 116 of FIG. 1 hasbeen decreased below the resonant frequency 132 to reduce the output ofthe sensor 116 of FIG. 1 to a level which is lower than the saturationlevel 134 of the electronic detection device 118 of FIG. 1 to avoidoversaturating the electronic detection device 118.

FIG. 3 illustrates a cross-section through one embodiment of a segmentof fluid delivery line 104 coupled to the electronic transmitting device114, the transmitter portion 116A of the sensor 116, the receiverportion 116B of the sensor 116, and the electronic detection device 118.The transmitter and receiver portions 116A and 116B of the sensor 116comprises piezoelectric crystals compressed against each side of thefluid delivery line 104 creating more surface area for uniform acousticcoupling and better signal to noise ratio. This arrangement of thetransmitter and receiver portions 116A and 116B of the sensor 116enables the transmission and detection of an ultrasonic signal through atarget volume of the fluid delivery line 104. The electronictransmitting device 114 generates a nominal 5.25 MHz ultrasonic signaldirected from the transmitter 116A portion of the sensor 116, throughthe fluid delivery line 104, to the receiver portion 116B of the sensor116 connected to the electronic detection device 118. When fluid ispresent in the fluid delivery line 104 at the position of the sensor116, the receiver portion 116B of the sensor 116 and the electronicdetection device 118 generate a larger electrical signal than when airis present at the same position. Because of an inversion in theelectronics of the electronic detection device 118, the software of theprocessing device 108 will receive a low signal when fluid is present atthe location of the sensor 116, and a high signal when air is present atthe location of the sensor 116. When a cassette is loaded into the pumpdevice 106, the segment of the fluid delivery line 104 distal to thecassette is clamped into place in front of the sensor 116. This enablesreliable and repeatable sensor performance over multiple cassettes.

FIG. 4 illustrates a top view through one embodiment of thepiezoelectric crystals of the transmitter portion 116A of the sensor 116of FIG. 3. As shown, the height Hof the transmitter portion 116Acomprises 0.100 inches and the width W of the transmitter portion 116Acomprises 0.100 inches. The dimensions of the receiver portion 116B ofthe sensor 116 of FIG. 1 are identical to the transmitter portion 116A.In other embodiments, the dimensions of the transmitter and receiverportions 116A and 116B of the sensor 116 may vary.

The ability of the ultrasonic signal to propagate from the transmitterportion 116A to the receiver portion 116B of the sensor 116 is governedby the acoustic impedance of the materials. The matching layers of thetransducers of the transmitter and receiver portions 116A and 116B aredesigned to control the amplitude of the reflections at thepiezo-matching layer and matching layer-fluid delivery line interfaces.The other significant component of the signal path is the fluid or airinside the fluid delivery line 104. The acoustic impedances (Za) @20° C.of interest are as follows: water=1.5×10⁶ kg/(m² s); PVC=3.3×10⁶ kg/(m²s); and air=413.2 kg/(m² s). Reflections of the ultrasonic signal occurat material boundaries and are governed by the differences in acousticimpedance. The reflection coefficient (RC) is defined as:RC=(Za−Zal)/(Za+Zal). A high RC indicates that the signal will not passthrough the boundary. For the PVC to water interface, the RC=0.375 whichindicates that a majority of the signal will pass through the interface.For the PVC to air interface, the RC=0.999 which indicates that anegligible, but non-zero portion of the signal energy will pass throughthe interface.

The electronic detection device 118 converts the signal received by thereceiver portion 116B of the sensor 116 from an analog signal to adigital electrical signal as governed by the equation: Vout=λ Tpiezoσ/Drvr, where Vout=the electrical signal received by the receiverportion 116B of the sensor; λ=the strain on the piezo crystal due to theultrasonic wave; σ=the stress on the piezo crystal due to the ultrasonicwave; Tpiezo=the thickness of the piezo crystal; Drvr=the mechanicaldisplacement of the piezo by the ultrasonic crystal. Thus, when fluid isin the fluid delivery line 104, the receiver portion 116B of the sensor116 is able to collect a large amount of ultrasonic energy since fluidis a better conductor than air. This appears as a low voltage at theanalog-to-digital converter of the electronic detection device 118because the signal received by the receiver portion 116B of the sensor116 is inverted electrically. The position of the fluid (for instance afluid droplet) inside the fluid delivery line 104 relative to thetransmitter and receiver portions 116A and 116B of the sensor 116 alsoinfluences the amount of energy the receiver portion 116B of the sensordetects. When air is in the fluid delivery line 104, the receiverportion 116B of the sensor 116 collects little energy.

The processing device 108 of FIG. 1 includes software components thatreceive the signal received by the receiver portion 116B of the sensor116 and converted to a digital signal though the electronic detectiondevice 118. The processing device 108 processes the received digitalsignal, and generates an alarm, using the alarm device 110 of FIG. 1,when the one or more algorithms stored in the programming code indicatesthat an amount of air over the air threshold is present.

FIG. 5 illustrates a flowchart of one embodiment of a method 140 forarranging and using an infusion system. The method 140 may utilize theinfusion system of FIG. 1. In other embodiments, the method 140 mayutilize varying systems. In step 142, a resonant frequency of at leastone sensor is determined. Step 142 may be done during calibration of theat least one sensor. In another embodiment, step 142 may be done at avarying time such as when in use in the field. In step 144, a saturationlevel of an analog-to-digital converter is determined. Step 144 may bedone during calibration of the analog-to-digital converter.Advantageously in another embodiment, step 144 may be done at a varyingtime such as when in use in the field. In step 146, the at least onesensor is disposed adjacent to a fluid delivery line. In one embodiment,step 146 may comprise disposing a transmitter portion of the at leastone sensor and a receiver portion of the at least one sensor on opposedsides of the fluid delivery line. In step 148, a pump is connected tothe fluid delivery line. In step 150, the analog-to-digital converter iselectronically connected to the at least one sensor. In step 152, atleast one processor is electronically connected to the pump, to the atleast one sensor, and to the analog-to-digital converter.

In step 154, the at least one processor is programmed to operate the atleast one sensor at a modified frequency which is different than theresonant frequency of the at least one sensor in order to reduce anamplitude of an output of a signal transmitted from the at least onesensor to a level which is lower than the saturation level of theanalog-to-digital converter to avoid over-saturating theanalog-to-digital converter. In one embodiment, step 154 may be doneduring calibration of the at least one sensor. Advantageously in anotherembodiment, step 154 may be done at a varying time such as when in usein the field. In still another embodiment, any or each of steps 142,144, and 154 may be done prior to steps 146, 148, 150, and 152.

In step 156, infusion fluid is pumped, with the pump, from an infusioncontainer through the fluid delivery line. In step 158, the signal istransmitted from the transmitter portion of the at least one sensor,while operating at the modified frequency which is different than theresonant frequency of the at least one sensor, through the fluiddelivery line. In step 160, the transmitted signal is received with thereceiver portion of the at least one sensor. In step 162, the signalreceived by the receiver portion of the at least one sensor is convertedfrom analog to digital using the analog-to-digital converter withoutover-saturating the analog-to-digital converter. In step 164, adetermination is made, using the at least one processor, whether air,fluid, or some combination thereof is in the fluid delivery line basedon the converted digital signal. In step 166, if the determination ismade in step 164 that air is disposed in the fluid delivery line, the atleast one processor turns on an alarm to indicate to a user that air isdisposed in the fluid delivery line. In one embodiment, if thedetermination is made in step 164 that air is disposed in the fluiddelivery line, then in step 166 the at least one processor turns on thealarm and shuts down the infusion system to stop the delivery ofinfusion fluid through the fluid delivery line. In other embodiments,the method 140 may be altered to vary the order or substance of any ofthe steps, to delete one or more steps, or to add one or more steps.

FIG. 6 illustrates a flowchart of one embodiment of a method 170 fordetecting air in a fluid delivery line of an infusion system. The method170 may utilize the infusion system of FIG. 1. In other embodiments, themethod 170 may utilize varying systems. In step 172, a saturation levelof an analog-to-digital converter may be determined. Step 172 may bedone during calibration of the analog-to-digital converter. In otherembodiments, step 172 may be done at a varying time such as when in usein the field. In step 174, a resonant frequency of at least one sensoris determined. Step 174 may be done during calibration of the at leastone sensor. Advantageously in other embodiments, step 174 may be done ata varying time such as when in use in the field. In step 176, a modifiedfrequency of the at least one sensor may be determined duringcalibration of the at least one sensor and the analog-to-digitalconverter to be different than the resonant frequency of the at leastone sensor to result in an amplitude of an output of the signaltransmitted from the at least one sensor being lower than the saturationlevel of the analog-to-digital converter to avoid over-saturating theanalog-to-digital converter. In other embodiments, step 176 may be doneat a varying time such as when in use in the field.

In step 178, infusion fluid is pumped through a fluid delivery lineadjacent to the at least one sensor. In step 180, a signal istransmitted and received, using the at least one sensor, into and fromthe fluid delivery line. Step 180 further comprises the at least onesensor operating, using at least one processor, at the modifiedfrequency which is different than the resonant frequency of the at leastone sensor in order to reduce an amplitude of an output of the signaltransmitted from the at least one sensor to a level which is lower thanthe saturation level of the analog-to-digital converter to avoidover-saturating the analog-to-digital converter. In one embodiment, step180 comprises transmitting the signal from a transmitter portion of theat least one sensor disposed on one side of the fluid delivery line,while operating at the modified frequency which is different than theresonant frequency of the at least one sensor, to a receiver portion ofthe at least one sensor disposed on an opposed side of the fluiddelivery line.

In step 182, the signal received by the at least one sensor is convertedfrom analog to digital using the analog-to-digital converter. In step184, a determination is made using the at least one processor whetherair, fluid, or some combination thereof is in the fluid delivery linebased on the converted digital signal. In step 186, if the determinationis made in step 184 that air is disposed in the fluid delivery line, theat least one processor turns on an alarm to indicate to a user that airis disposed in the fluid delivery line. In one embodiment, if thedetermination is made in step 184 that air is disposed in the fluiddelivery line, then in step 186 the at least one processor turns on thealarm and shuts down the infusion system to stop the delivery ofinfusion fluid through the fluid delivery line. In other embodiments,the method 170 may be altered to vary the order or substance of any ofthe steps, to delete one or more steps, or to add one or more steps.

FIG. 7 is a graph 190 illustrating five different curves 192, 194, 196,198, and 200 showing for five different illustrative sensors, whichcould each be tried for the sensor 116 in the infusion system of FIG. 1,how their respective signal strength varies as their modified frequencyvaries. The frequency performance for each sensor is plotted on theX-axis of the graph 190. The signal output of each sensor is plotted onthe Y-axis of the graph 190. The electronic detection device 118 of FIG.1 requires a minimum useful signal strength of greater than or equal to100 mVpp. The electronic detection device 118 of FIG. 1 isover-saturated when the output of any of the sensors exceeds thesaturation level 202 which is approximately 750 mVpp.

Curve 192 has a sensor output of below the minimum useful signal of 100mVpp no matter how the modified frequency is varied. As a result thissensor should not be used because the signal is too weak. Curve 194 hasa sensor output of below the minimum useful signal of 100 mVpp at somemodified frequencies, and a sensor output of greater than or equal tothe minimum useful signal of 100 mVpp at other modified frequencies yetthe entire curve is below the saturation level 202 of 750 mVpp. As aresult, this sensor can be used at any modified frequency which resultsin a signal output of greater than or equal to the minimum useful signalof 100 mVpp which is in the approximate range of between 4.3 MHz to 5.7MHz as shown by curve 194. Curve 196 has a sensor output of below theminimum useful signal of 100 mVpp at some modified frequencies, and asensor output of greater than or equal to the minimum useful signal of100 mVpp at other modified frequencies yet the entire curve is below thesaturation level 202 of 750 mVpp. As a result, this sensor can be usedat any modified frequency which results in a signal output of greaterthan or equal to the minimum useful signal of 100 mVpp which is in theapproximate range of between 4.2 MHz to 5.8 MHz as shown by curve 196.

Curve 198 has a sensor output of below the minimum useful signal of 100mVpp at some modified frequencies, and a sensor output of greater thanor equal to the minimum useful signal of 100 mVpp at other modifiedfrequencies. Additionally, curve 198 has a sensor output of below thesaturation level 202 of 750 mVpp at some modified frequencies, and asensor output of above the saturation level 202 of 750 mVpp at othermodified frequencies. As a result, this sensor can be used at anymodified frequency which results in a signal output of greater than orequal to the minimum useful signal of 100 mVpp and results in a signaloutput of less than the saturation level 202 of 750 mVpp which is in theapproximate range of between 3.4 MHz to 5.9 MHz as shown by curve 198.In order to obtain a modified frequency which results in a signal outputof greater than or equal to the minimum useful signal of 100 mVpp andresults in a signal output of less than the saturation level 202 of 750mVpp, Applicants have discovered that the modified frequency for curve198 needs to be within ±36% from the resonant frequency 199 of 5.3 MHzand within ±31% from the minimum or maximum saturation frequencies 201and 203 which result in the saturation level of 750 mVpp. Preferably,the highest modified frequency is selected which results in a signaloutput as high as possible without exceeding the saturation level and isabove the minimum useful signal strength.

Curve 200 has a sensor output of below the minimum useful signal of 100mVpp at some modified frequencies, and a sensor output of greater thanor equal to the minimum useful signal of 100 mVpp at other modifiedfrequencies. Additionally, curve 200 has a sensor output of below thesaturation level 202 of 750 mVpp at some modified frequencies, and asensor output of above the saturation level 202 of 750 mVpp at othermodified frequencies. As a result, this sensor can be used at anymodified frequency which results in a signal output of greater than orequal to the minimum useful signal strength of 100 mVpp and results in asignal output of less than the saturation level 202 of 750 mVpp which isin the approximate range of between 3.5 MHz to 6.0 MHz as shown by curve200. In order to obtain a modified frequency which results in a signaloutput of greater than or equal to the minimum useful signal of 100 mVppand results in a signal output of less than the saturation level 202 of750 mVpp, Applicants have discovered that the modified frequency forcurve 200 needs to be within ±34% from the resonant frequency 205 of 5.3MHz and within ±27% from the minimum or maximum saturation frequencies207 and 209 which result in the saturation level of 750 mVpp.Preferably, the highest modified frequency is selected which results ina signal output as high as possible without exceeding the saturationlevel and which is above the minimum useful signal strength. In oneembodiment, this modified frequency may be chosen so that the signaloutput is within 5% of the saturation level. In another embodiment, thismodified frequency may be chosen so that the signal output is within 10%of the saturation level. In other embodiments, varied modifiedfrequencies may be chosen.

In other embodiments, other sensors may be used which have differentsensor signal strength performance at varied modified frequencies. Inone embodiment, a sensor may be used which has a modified frequency ofwithin ±50% from the resonant frequency and within ±50% from asaturation frequency. In another embodiment, a sensor may be used whichhas a modified frequency of within ±40% from the resonant frequency andwithin ±40% from a saturation frequency. In another embodiment, a sensormay be used which has a modified frequency of within ±30% from theresonant frequency and within ±30% from a saturation frequency. Inanother embodiment, a sensor may be used which has a modified frequencyof within ±20% from the resonant frequency and within ±20% from asaturation frequency. In another embodiment, a sensor may be used whichhas a modified frequency of within ±10% from the resonant frequency andwithin ±10% from a saturation frequency.

FIG. 8 illustrates a flowchart of one embodiment of a method 210 fordetermining the modified frequency of an infusion system. The method 210may utilize the infusion system of FIG. 1. In other embodiments, themethod 210 may utilize varying systems. The method 210 may beincorporated into any of the other methods disclosed herein includingthe methods illustrated in FIGS. 5 and 6 of this disclosure. In step212, a determination is made as to whether the maximum signal output ofthe sensor at any modified frequency is greater than or equal to theminimum useful signal strength required by the electronic detectiondevice. If the determination is made in step 212 that the maximum signaloutput of the sensor at any modified frequency is not greater than orequal to the minimum useful signal strength then in step 213 a newsensor is chosen and then step 212 is repeated until the determinationis made in step 212 that the maximum signal output of the sensor at anymodified frequency is greater than or equal to the minimum useful signalstrength. Once the determination is made in step 212 that the maximumsignal output of the sensor at any modified frequency is greater than orequal to the minimum useful signal strength, then the method proceedsfrom step 212 to step 214.

In step 214, a determination is made as to whether the signal output ofthe sensor at the resonant frequency is less than the saturation levelof the electronic detection device. If the determination is made in step214 that the signal output of the sensor at the resonant frequency isless than the saturation level of the electronic detection device, thenthe method proceeds to step 216. In step 216, the sensor is operated ata modified frequency which is equal to the resonant frequency of thesensor.

If the determination is made in step 214 that the signal output of thesensor at the resonant frequency is not less than the saturation levelof the electronic detection device, then the method proceeds to step218. In step 218, the sensor is operated at a modified frequency whichresults in a signal output which is less than the saturation level ofthe electronic detection device but greater than the minimum usefulsignal strength of the electronic detection device. Preferably, in step218 the sensor is operated at the highest modified frequency whichresults in a signal output as high as possible without exceeding thesaturation level of the electronic detection device and which is abovethe minimum useful signal strength of the electronic detection device.In one embodiment of step 218, the sensor may be operated at a modifiedfrequency within 5% of the saturation level. In another embodiment ofstep 218, the sensor may be operated at a modified frequency within 10%of the saturation level. In other embodiments of step 218, the sensormay be operated at varied modified frequencies. In other embodiments,the method 210 may be altered to vary the order or substance of any ofthe steps, to delete one or more steps, or to add one or more steps.

One or more embodiments of the disclosure may improve the accuracy andreliability of the detection of air in infusion systems. One or moreembodiments of the disclosure may be incorporated during calibration ofone or more components of the infusion system. One or more embodimentsof the disclosure may be done in the field without having to replaceexisting sensors of the infusion system by performing a field serviceprocedure. This reduces the cost of sensor replacement and reduces theamount of replacement parts that must be kept in inventory. Thedisclosure also can accommodate greater variability and thus increasesthe yield of sensor assemblies that can be used.

The Abstract is provided to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin various embodiments for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separately claimed subject matter.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true scope of the subject matter described herein.Furthermore, it is to be understood that the disclosure is defined bythe appended claims. Accordingly, the disclosure is not to be restrictedexcept in light of the appended claims and their equivalents.

1.-20. (canceled)
 21. An infusion system configured to improve detectionof air in a fluid delivery line, the infusion system comprising: asensor configured to detect a first signal transmitted in a fluiddelivery line; an analog-to-digital converter electronically connectedto the sensor, the analog-to-digital converter configured to convert thedetected signal from analog to digital; a hardware processor connectedwith the analog-to-digital converter, the hardware processor configuredto: determine that the detected first signal is saturated; change anoperating frequency of the sensor based on the determination ofsaturation; transmit a second signal at the changed operating frequency;and determine air in the fluid delivery line based on the transmittedsecond signal.
 22. The infusion system of claim 21, wherein the changedoperating frequency is different than a resonant frequency of thesensor.
 23. The infusion system of claim 21, wherein the one or morehardware processors are further configured to determine the resonantfrequency of the sensor.
 24. The infusion system of claim 21, whereinthe one or more hardware processors are further configured to determinea minimum level for received signals.
 25. The infusion system of claim24, wherein the one or more hardware processors are further configuredto change the operating frequency to exceed the minimum level forreceived signals.
 26. The infusion system of claim 21, wherein thechanged operating frequency is within ±50% of the resonant frequency.27. An method of improving detection of air in a fluid delivery line,the method comprising: detecting a first signal transmitted in a fluiddelivery line; converting the detected signal from analog to digital;determining that the detected first signal is saturated; changing anoperating frequency of the sensor based on the determination ofsaturation; transmitting a second signal at the changed operatingfrequency; and determining air in the fluid delivery line based on thetransmitted second signal.
 28. The method of claim 27, wherein thechanged operating frequency is different than a resonant frequency ofthe sensor.
 29. The method of claim 27, further comprising the resonantfrequency of the sensor.
 30. The method of claim 27, further comprisingdetermining a minimum level for received signals.
 31. The method ofclaim 30, further comprising changing the operating frequency to exceedthe minimum level for received signals.
 32. The method of claim 27,wherein the changed operating frequency is within ±50% of the resonantfrequency.
 33. An infusion system configured to improve detection of airin a fluid delivery line, the infusion system comprising one or morehardware processors configured to: receive a first digital signalcorresponding to a first signal detected by a sensor, wherein the firstsignal is responsive to a transmitted signal in a fluid delivery line;determine that the first digital signal is saturated; change anoperating frequency of the sensor based on the determination ofsaturation; transmit a second signal at the changed operating frequency;and determine air in the fluid delivery line based on the transmittedsecond signal.
 34. The infusion system of claim 33, wherein the changedoperating frequency is different than a resonant frequency of thesensor.
 35. The infusion system of claim 33, wherein the one or morehardware processors are further configured to determine the resonantfrequency of the sensor.
 36. The infusion system of claim 33, whereinthe one or more hardware processors are further configured to determinea minimum level for received signals.
 37. The infusion system of claim36, wherein the one or more hardware processors are further configuredto change the operating frequency to exceed the minimum level forreceived signals.
 38. The infusion system of claim 33, wherein thechanged operating frequency is within ±50% of the resonant frequency.